Oil pump

ABSTRACT

An oil pump including an upstream pump unit including an upstream inner rotor and an upstream outer rotor; a downstream pump unit including a downstream inner rotor and a downstream outer rotor as being arranged adjacently to the upstream pump unit in a predetermined axis line direction; a rotary shaft concurrently rotating the upstream inner rotor and the downstream inner rotor; and a housing which contains the upstream pump unit and the downstream pump unit as supporting the rotary shaft and which includes an inlet port for sucking oil from the outside into the upstream pump unit, an ejection port for ejecting a part thereof to the outside in a pressurization process of the upstream pump unit, a communication port for providing communication between the upstream pump unit and the downstream pump unit, and a discharge port for discharging oil from the downstream pump unit to the outside.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the foreign priority benefit of Japanese Patent Application No. 2012-0953901, filed Apr. 19, 2012, in the Japanese Intellectual Property Office, the disclosure of which is incorporated herein by reference.

BACKGROUND

1. Field

The present invention relates to an oil pump which sucks and discharges oil (lubricant oil) of an internal combustion engine (hereinafter, called an engine) or the like, and in particular, relates to an oil pump including an inner rotor and an outer rotor of a trochoid type, an internal gear type (involute type), or the like.

2. Description of the Related Art

There has been known an oil pump for an engine including a housing which has an inlet port for sucking oil, a discharge port for discharging oil, an air vent hole (an ejection port, or a deairing port) for ejecting air mixed with oil and the like, a rotary shaft (drive shaft) which is supported by the housing, an inner rotor which is rotated by the rotary shaft and which has external teeth, an outer rotor which has internal teeth engaged with the external teeth of the inner rotor and which defines a volume-varying pump chamber in cooperation with the inner rotor, and the like. Here, pumping action is obtained by rotating the inner rotor via the rotary shaft and rotating the outer rotor as being coordinated with the rotation of the inner rotor, so that oil sucked through the inlet port is pressurized and discharged through the discharge port while air (bubble) mixed with oil is ejected through the air vent hole. For example, see Japanese Patent Application No. 9-203308, Japanese Patent Application No. 6-167278, and Japanese Patent Application No. 4-65974.

Since the above conventional oil pumps are a one-stage pressurization type having only one set of pump unit which includes the inner rotor and the outer rotor, there is a fear that required discharge pressure may not be satisfied depending on an engine to which the oil pump is adopted.

Meanwhile, there has been known a fluid pump capable of ensuring high discharge pressure including a housing which has one or two inlet ports for sucking oil from the outside and one discharge port for discharging oil to the outside, a rotary shaft (drive shaft) which is supported by the housing, and a prior-stage pump unit and a latter-stage pump unit arranged in an axial direction of the rotary shaft. Here, the prior-stage pump unit is structured with one set or two sets of an inner rotor (inner gear) and an outer rotor (outer gear) and the latter-stage pump unit is structured with one set of an inner rotor (inner gear) and an outer rotor (outer gear). A discharge rate of the prior-stage pump unit and a discharge rate of the latter-stage pump unit are set to be the same. Pumping action at the first stage due to the prior-stage pump unit and pumping action at the second stage due to the latter-stage pump unit are obtained by rotating the prior-stage and latter-stage inner rotors (inner gears) via the rotary shaft and rotating the prior-stage and latter-stage outer rotors (outer gears) as being coordinated with the rotation of the inner rotors (inner gears). Fluid is pressurized as being sucked through the inlet port and double-pressurized fluid is discharged through the discharge port. For example, see Japanese Patent Application No. 2007-127071.

In the above two-stage pressurization type fluid pump, the discharge rate (discharge pressure) of the prior-stage pump unit and the discharge rate (discharge pressure) of the latter-stage pump unit are simply set to be the same without considering influence on discharge characteristics when air or the like is mixed with fluid to be sucked. Therefore, there is a fear that desired discharge characteristics (discharge rate) cannot be ensured when air or the like is mixed.

SUMMARY

Additional aspects and/or advantages will be set forth in part in the description which follows and, in part, will be apparent from the description, or may be learned by practice of the invention.

To address the above issues, the present invention provides an oil pump which ensures desired pumping performance even if air or the like is mixed with oil to be sucked and provides pumping characteristics having desired high discharge pressure (discharge rate).

An oil pump according to the present invention includes an upstream pump unit which includes an upstream inner rotor and an upstream outer rotor; a downstream pump unit which includes a downstream inner rotor and a downstream outer rotor as being arranged adjacently to the upstream pump unit in a predetermined axis line direction; a rotary shaft which concurrently rotates the upstream inner rotor and the downstream inner rotor; and a housing which contains the upstream pump unit and the downstream pump unit as supporting the rotary shaft and which includes an inlet port configured to suck oil from the outside into the upstream pump unit, an ejection port configured to eject a part of the sucked oil to the outside in a pressurization process of the upstream pump unit, a communication port which provides communication between the upstream pump unit and the downstream pump unit, and a discharge port configured to discharge oil from the downstream pump unit to the outside.

According to the above structure, in a case that the oil pump is mounted on an engine for sucking and pressure-feeding oil (lubricant oil) in an oil pan, oil is sucked into the pump chamber due to pumping action of the upstream pump unit (the upstream inner rotor and the upstream outer rotor), and then, the sucked air-mixed oil is returned to the oil pan as being ejected outside through the ejection port while being pressurized. Subsequently, remaining oil is pressurized to predetermined pressure (e.g., 3.0 MPa) and supplied from the upstream pump unit to the downstream pump unit (the downstream inner rotor and the downstream outer rotor) through the communication port. Subsequently, the oil is sucked into the pump chamber of the downstream pump unit with pumping action thereof and is further pressurized to predetermined pressure (e.g., 6.0 MPa). Then, the oil is discharged outside through the discharge port toward various lubrication areas.

Here, the ejection port for ejecting air-mixed oil is formed as being faced to the upstream pump unit at the first stage. Since the density (mass) of the air (bubble) mixed with the oil is small, air is easily collected at the inner side of the pump chamber by the action of centrifugal separation. Accordingly, mixed air can be effectively ejected.

In the above structure, the upstream pump unit may be configured to have a discharge rate being larger than a discharge rate of the downstream pump unit.

According to the above, since the discharge rate of the upstream pump unit to which the ejection port is faced is larger than the discharge rate of the downstream pump unit, oil can be discharged at a desired discharge rate from the downstream pump unit even when air-mixed oil is discharged through the ejection port.

In the above structure, the upstream pump unit may have a discharge rate equal to a sum of a discharge rate of the downstream pump unit and an ejection rate ejected through the ejection port.

According to the above, since the discharge rates of the upstream pump unit and the downstream pump unit are set in consideration of the return rate (ejection rate) to be returned to the oil pan through the ejection port, oil can be supplied (discharged) outside at the desired discharge rate while achieving high pressurization with two-stage pressurizing action.

In the above structure, the ejection rate ejected through the ejection port may be set to be 20% or more of the discharge rate of the upstream pump unit.

According to the above, air (bubble) mixed with oil in the suction process of the upstream pump unit can be ejected more effectively.

In the above structure, the upstream pump unit may be configured to have a thickness in the axis line direction being larger than a thickness of the downstream pump unit in the axis line direction.

According to the above, the discharge rate of the upstream pump unit can be easily set to be larger than the discharge rate of the downstream pump unit while basic specifications of the upstream inner rotor and the upstream outer rotor are kept the same as those of the downstream inner rotor and the downstream outer rotor only by differentiating the thicknesses thereof in the axis line direction.

The housing may include a housing body which includes a concave portion for containing the upstream pump unit and the downstream pump unit, a partition member which is interposed between the upstream pump unit and the downstream pump unit, and a housing cover with which the housing body is covered.

According to the above, desired pumping characteristics can be ensured while achieving downsizing. Further, assembling operation can be easily performed such that the upstream pump unit, the partition member, and the downstream pump unit are contained in the housing body and that the housing cover is attached thereon.

In the above structure, the ejection port may be arranged at the housing cover, the communication port may be arranged at the partition member, and the inlet port may be arranged at the partition member at a position opposite to the ejection port in the axis line direction as sandwiching the upstream pump unit.

According to the above, oil sucked through the inlet port can be reliably pressurized in the upstream pump unit while ejecting mixed air through the ejection port, and then, remaining pressurized oil can be supplied to the downstream pump unit through the communication port. As a whole, pumping performance can be improved.

In the above structure, each of the upstream pump unit and the downstream pump unit is a trochoid type having four blades and five nodes with the inner rotor and the outer rotor.

According to the above, a desired high discharge rate can be ensured while effectively ejecting mixed air. Accordingly, pumping performance and durability can be improved.

According to the oil pump having the above structure, desired pumping performance can be ensured even if air or the like is mixed with oil to be sucked and pumping characteristics having desired high discharge pressure (discharge rate) can be obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

These and/or other aspects and advantages will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which:

FIG. 1 is a schematic view of an oil pump according to the present invention;

FIG. 2 is a front view illustrating an embodiment of the oil pump according to the present invention;

FIG. 3 is a sectional view illustrating the inside of the oil pump illustrated in FIG. 2;

FIG. 4 is a front view illustrating a housing body which structures a part of the oil pump illustrated in FIG. 2;

FIG. 5A is a plane view of a housing cover which structures a part of the oil pump illustrated in FIG. 2 viewed from the rear R side (inner surface side);

FIG. 5B is a sectional view at E1-E1 in FIG. 5A;

FIG. 6 is a sectional view illustrating a rotor case which structures a part of the oil pump illustrated in FIG. 2;

FIG. 7A is an end view of the rotor case illustrated in FIG. 6 viewed from the front F side;

FIG. 7B is an end view of the rotor case viewed from the rear R side;

FIG. 8A is a plane view of a side plate which structures a part of the oil pump illustrated in FIG. 2 viewed from the front F side;

FIG. 8B is a sectional view at E2-E2 in FIG. 8A;

FIG. 9A is a plane sectional illustrating a part of the oil pump illustrated in FIG. 2 viewing an upstream pump unit (a first inner rotor and a first outer rotor) from the rear R side; and

FIG. 9B is a sectional view illustrating a part of the oil pump viewing a downstream pump unit (a second inner rotor and a second outer rotor) from the front F side.

DETAILED DESCRIPTION

In the following, embodiments of the present invention will be described with reference to the attached drawings.

As illustrated in FIGS. 1 to 3, an oil pump according to an embodiment includes a housing body 10 and a housing cover 20 which constitute a housing H, a rotary shaft 30 which is supported by the housing H as being rotatable about an axis line S, a rotor case 40 which is assembled in the housing H, a side plate 50 which is in contact with an end face of the rotor case 40, an O-ring 60 which urges the side plate 50 toward the rotor case 40 in the direction of the axis line S, an upstream pump unit 70 (a first inner rotor 71 and a first outer rotor 72) which is contained in the rotor case 40, a downstream pump unit 80 (a second inner rotor 81 and a second outer rotor 82) which is contained in the rotor case 40 as being adjacent to the upstream pump unit 70 in the direction of the axis line S, and the like.

Here, the rotor case 40 and the side plate 50 are formed separately from the housing H and constitute a part of the housing H for containing the upstream pump unit 70 and the downstream pump unit 80.

The housing body 10 is made of aluminum material for weight saving and is configured to form a concave portion for containing the upstream pump unit 70 and the downstream pump unit 80 along with the rotor case 40. As illustrated in FIGS. 3 and 4, the housing body 10 includes a bearing hole 11 for rotatably supporting one end portion 31 of the rotary shaft 30 via a bearing G, a cylindrical inner circumferential face 12 to which the rotor case 40 is fitted, two circular end faces 13 which are formed around the bearing hole 11 as having diameters lessened to form a stepped portion at a back side of the inner circumferential face 12, an inlet passage 14 through which oil is sucked as being formed by removing a part of the inner circumferential face 12 and drilling thereat outward in the radial direction, a discharge passage 15 through which pressurized oil is discharged as being formed at a bottom side, a positioning hole 16 for positioning the side plate 50, a joint face 17 for joining the housing cover 20, screw holes 18 into which bolts B are screwed for fastening the housing cover 20, positioning holes 19 for positioning the housing cover 20, and the like.

The housing cover 20 is made of aluminum material the same as the housing body 10 for weight saving. As illustrated in FIGS. 2, 3, 5A and 5B, the housing cover 20 includes a bearing hole 21 for rotatably supporting the other end 32 of the rotary shaft 30 via a bearing G, a concave portion 22 which is faced to a later-mentioned inlet port 44 b in the direction of the axis line S, a concave portion 23 which is faced to a later-mentioned communication port 44 e in the direction of the axis line S, an ejection port 24 through which air mixed with sucked oil (air-mixed oil) is ejected, circular holes 25 through which the bolts B pass, positioning holes 26 for performing positioning to the housing cover 10, a positioning hole 27 for positioning the rotor case 40, and the like.

The housing cover 20 is joined to the joint face 17 while a positioning pin fitted into the positioning hole 19 is fitted into the positioning pin 26 and a positioning pin fitted into a positioning hole 45 a of the rotor case 40 is fitted into the positioning hole 27. Then, the housing cover 20 is fixed to the housing body 10 by screwing the bolts B into the screw holes 18 as passing through the circular holes 25 from the outer side. Thus, the housing cover 20 closes opening of the housing body 10.

As illustrated in FIGS. 5A and 5B, the ejection port 24 is formed as being faced to the upstream pump unit 70. Further, the ejection port 24 is opened to be approximately L-shaped as being elongated in the radial direction of the bearing hole 21 and being elongated in a rotation direction (an arrow direction in FIG. 1) of the upstream pump unit 70 (the first inner rotor 71 and the first outer rotor 72) at a vicinity of an outer edge thereof in the radial direction.

As described above, the ejection port 24 for ejecting air-mixed oil is formed as being faced to the upstream pump unit 70 at the first stage. Since density (mass) of air (bubble) mixed with oil is small, air is easily collected at the inner side of a pump chamber P by the action of centrifugal separation. Accordingly, mixed air can be effectively ejected.

Here, the ejection port 24 is not limited to have the abovementioned shape. It is also possible to adopt an appropriate shape in accordance with a target ejection rate of air-mixed oil.

As illustrated in FIG. 3, the rotary shaft 30 made of steel or the like is formed as being elongated in the direction of the axis line S. The rotary shaft 30 includes the one end portion 31 which is supported by the bearing hole 11 of the housing body 10 via the bearing G, the other end portion 32 which is supported by the bearing hole 21 of the housing cover 20 via the bearing G, a shaft portion 33 which integrally rotates the first inner rotor 71 of the upstream pump unit 70, a shaft portion 34 which integrally rotates the second inner rotor 81 of the downstream pump unit 80, a shaft portion 35 which is supported by the bearing G, and the like. The rotary shaft 30 is configured to be rotationally driven as being connected to a rotary member of an engine.

The rotor case 40 is made of steel, casting iron, sintered steel, or the like. As illustrated in FIGS. 3, 6 and 7, the rotor case 40 includes a cylindrical portion which is centered at the axis line S, an inner circumferential face 42 centered at an axis line L1 which is shifted by a predetermined amount from the axis line S at the inner side of the cylindrical portion 41, an inner circumferential face 43 centered at an axis line L2 which is shifted by a predetermined amount from the axis line S at the inner side of the cylindrical portion 41, a middle wall portion 44 as a partition member formed between the inner circumferential face 42 and the inner circumferential face 43 in the direction of the axis line S, a bearing hole 44 a arranged at the middle wall portion 44, an inlet port 44 b which is arranged at the middle wall portion 44, an upstream discharge port 44 c (of the upstream pump unit 70) which is arranged at the middle wall portion 44, a downstream inlet port 44 d (of the downstream pump unit 80) which is arranged at the middle wall portion 44, the communication port 44 e through which the upstream discharge port 44 c and the downstream inlet port 44 d are mutually connected, an end face 45 with which the housing cover 20 is in contact, a positioning hole 45 a which is formed at the end face 45, an end face 46 with which the side plate 50 is in contact, a positioning hole 46 a which is formed at the end face 46, and the like.

The cylindrical portion 41 is formed to have an outer diameter dimension so that the cylindrical portion 41 is fitted into the housing body 10 as being capable of relatively moving in the direction of the axis line S in accordance with difference between thermal deformation (expansion and contraction) amounts of the housing body 10 and the rotor case 40 while being intimately contacted to the inner circumferential face of the housing body 10.

The inner circumferential face 42 is formed to have a dimension so that the first outer rotor 72 of the upstream pump unit 70 is in contact with the inner circumferential face 42 rotatably (slidably) about the axis line L1.

The inner circumferential face 43 is formed to have a dimension so that the second outer rotor 82 of the downstream pump unit 80 is in contact with the inner circumferential face 43 rotatably (slidably) about the axis line L2.

The inlet port 44 b is formed so as to be faced to a pump chamber P of the upstream pump unit 70 while communicating with the inlet passage 14.

Thus, the inlet port 44 b is arranged at the middle wall portion 44 as being located at the opposite side to the ejection port 24 while sandwiching the upstream pump unit 70 in the direction of the axis line S. Accordingly, oil sucked through the inlet port 44 b can be reliably pressurized in the upstream pump unit 70 and is supplied to the downstream pump unit 80 through the communication port 44 e. As a whole, pumping performance can be improved.

The communication port 44 e is configured to cause communication between the upstream discharge port 44 c and the downstream inlet port 44 d so that oil discharged from the upstream pump unit 70 is introduced to the downstream pump unit 80.

The rotor case 40 is assembled (fitted) to the inner circumferential face 12 of the housing body 10 in a state of containing the upstream pump unit 70 at the inner circumferential face 42 and the downstream pump unit 80 at the inner circumferential face 43 along with the rotary shaft 30 while the positioning pin fitted into the positioning hole 16 is fitted into the positioning hole 46 a as sandwiching the O-ring 60 and the side plate 50 in cooperation with the end face 13.

The side plate 50 is formed disc-shaped and is made of steel, casted iron, sintered steel, aluminum alloy, or the like. As illustrated in FIGS. 3 and 8, the side plate 50 includes a circular hole 51 through which the rotary shaft 30 passes, a discharge port 52 through which oil pressurized by the downstream pump unit 80 is discharged, a positioning hole 53, a concave portion 54 which receives one end side of the bearing G, and the like.

The side plate 50 is configured to be assembled to the housing body 10 as sandwiching the O-ring 60 at a space against the end face 13 while positioning pin fitted into the positioning hole 16 of the housing body 10 passes through the positioning hole 53.

The O-ring 60 is formed circularly of elastically-deformable rubber material or the like and is arranged between the end face 13 of the housing body 10 and the side plate 50. The fi-ring 60 is assembled as being compressed by a predetermined compression amount in the direction of the axis line S to urge the side plate 50 toward the end face 46 of the rotor case 40.

The upstream pump unit 70 is made of steel, sintered steel, or the like. As illustrated in FIG. 9A, the upstream pump unit 70 is a trochoid pump having four blades and five nodes with the first inner rotor 71 and the first outer rotor 72.

The first inner rotor 71 is formed as an external gear which has four crests (external teeth) and roots (cavities) while including a fitting hole 71 a into which the shaft portion 33 of the rotary shaft 30 is fitted.

The first outer rotor 72 is formed as an internal gear which has five crests (inner teeth) and roots (cavities) to be engaged with the four crests (external teeth) and roots (cavities) of the first inner rotor 71 at the inner circumference thereof while including an outer circumferential face 72 a which is slidably fitted to the inner circumferential face 42 of the rotor case 40.

When the first inner rotor 71 is rotated along with the rotary shaft 30 in an arrow direction about the axis line S (counterclockwise in FIG. 9A), the first outer rotor 72 is coordinated and rotated in an arrow direction about the axis line L1 (counterclockwise in FIG. 9A). Accordingly, volume of the pump chamber P defined by both thereof is varied and oil is sucked through the inlet port 44 b and pressurized subsequently. Air-mixed oil is ejected through the ejection port 24 in the pressurization process, and subsequently, remaining oil is discharged through the upstream discharge port 44 c to the downstream pump unit 80. Then, the above processes are to be repeated.

The downstream pump unit 80 is made of steel, sintered steel, or the like. As illustrated in FIG. 9B, the downstream pump unit 80 is a trochoid pump having four blades and five nodes including the second inner rotor 81 and the second outer rotor 82.

The second inner rotor 81 is formed as an external gear which has four crests (external teeth) and roots (cavities) while including a fitting hole 81 a into which the shaft portion 34 of the rotary shaft 30 is fitted.

The second outer rotor 82 is formed as an internal gear which has five crests (inner teeth) and roots (cavities) to be engaged with the four crests (external teeth) and roots (cavities) of the second inner rotor 81 at the inner circumference thereof while including an outer circumferential face 82 a which is slidably fitted to the inner circumferential face 43 of the rotor case 40.

When the second inner rotor 81 is rotated along with the rotary shaft 30 in an arrow direction about the axis line S (clockwise in FIG. 9B), the second outer rotor 82 is coordinated and rotated in an arrow direction about the axis line L2 (clockwise in FIG. 9B). Accordingly, volume of the pump chamber P defined by both thereof is varied and oil is sucked through the downstream inlet port 44 d and pressurized subsequently. Then, oil is discharged through the discharge port 52 toward an external lubrication area. The above processes are to be repeated.

The above structure is configured to satisfy an expression of “Qu=Qd+Qe” while Qu, Qd, and Qe denote a discharge rate (suction rate) of the upstream pump unit 70, a discharge rate (suction rate) of the downstream pump unit 80, and an ejection rate (of air-mixed oil) ejected through the ejection port 24, respectively.

In this manner, since the discharge rates Qu, Qd are set in consideration of the return rate (ejection rate Qe) to be returned to an oil pan OP through the ejection port 24, oil can be supplied (discharged) outside at the desired discharge rate Qd while achieving high pressurization with two-stage pressurizing action.

Here, it is preferable that the ejection rate Qe ejected through the ejection port 24 is set in a range between 20% and 50% inclusive of the discharge rate Qu of the upstream pump unit 70.

With the above, air (bubble) mixed with oil in the suction process of the upstream pump unit 70 can be ejected more effectively.

Further, as illustrated in FIG. 6, the above structure is configured to satisfy an expression of “Wu>Wd” while Wu denoting a thickness of the upstream pump unit 70 in the direction of the axis line S and Wd denoting a thickness of the downstream pump unit 80 in the direction of the axis line S.

Owing to arrangement of the thicknesses Wu, Wd in the direction of the axis line S, the discharge rate Qu of the upstream pump unit 70 can be easily set to be larger than the discharge rate Qd of the downstream pump unit 80 while basic specifications of the upstream inner rotor 71 and the upstream outer rotor 72 are kept the same as those of the downstream inner rotor 81 and the downstream outer rotor 82.

In a case that the oil pump having the above structure is mounted on an engine with the oil pan OP, as illustrated in FIG. 1, oil (lubricant oil) is firstly sucked into the pump chamber P due to pumping action of the upstream pump unit 70, and then, the sucked air-mixed oil is returned to the oil pan OP as being ejected outside through the ejection port 24 while being pressurized. Subsequently, remaining oil is pressurized to predetermined pressure (e.g., 3.0 MPa) and supplied from the upstream pump unit 70 to the downstream pump unit 80 through the communication port 44 e. Subsequently, the oil is sucked into the pump chamber P of the downstream pump unit 80 with pumping action thereof and is further pressurized to predetermined pressure (e.g., 6.0 MPa). Then, the oil is discharged outside through the discharge port 52 toward various lubrication areas.

In the above structure, the housing body 10 and the housing cover 20 form the housing H and the rotor case 40 defining the middle wall portion 44 as the partition member separately contains the upstream pump unit 70 and the downstream pump unit 80 in advance. Accordingly, for assembling the oil pump, it is only required to place the upstream pump unit 70 and the downstream pump unit 80 into the rotor case 40 along with the rotary shaft 30, to sequentially place the O-ring 60, the side plate 50, and the rotor case 40 into the housing body 10, and then, to attach the housing cover 20 thereon. In this manner, assembling operation can be easily performed.

Next, operation of the oil pump will be described with reference to FIGS. 9A and 9B.

First, when the rotary shaft 30 is rotationally driven by an engine, the upstream pump unit 70 (the first inner rotor 71 and the first outer rotor 72) is rotated counterclockwise in FIG. 9A and oil is sucked into the pump chamber P of the upstream pump unit 70 through the inlet passage 14 and the inlet port 44 b.

Owing to continuous rotation of the upstream pump unit 70, the oil sucked into the pump chamber P is pressurized. In the pressurization process, air-mixed oil is forcedly ejected outside through the ejection port 24 at the predetermined ejection rate Qe. Further, the remaining oil (Qu−Qe) obtained by subtracting the ejection rate Qe from the discharge rate Qu is discharged (supplied) as being pressurized to predetermined discharge pressure (about 3.0 MPa) toward the downstream pump unit 80 through the upstream discharge port 44 c, the communication port 44 e, and the downstream inlet port 44 d.

Subsequently, the oil is sucked into the pump chamber P of the downstream pump unit 80 through the downstream inlet port 44 d with clockwise rotation in FIG. 9B of the downstream pump unit 80 (the second inner rotor 81 and the second outer rotor 82).

Owing to continuous rotation of the downstream pump unit 80, the oil sucked into the pump chamber P is pressurized and discharged (supplied) toward an external lubrication area through the discharge port 52 and the discharge passage 15 at predetermined discharge pressure (about 6.0 MPa) and the predetermined discharge rate (discharge rate Qd).

Practically, cooperative action of the upstream pump unit 70 (the first inner rotor 71 and the first outer rotor 72) and the downstream pump unit 80 (the second inner rotor 81 and the second outer rotor 82) causes continuously operation of a series of processes, that is, sucking oil from the oil pan OP at the first stage, pressurizing oil at the first stage, ejecting mixed air and oil (air-mixed oil) at the first stage, discharging remaining oil at the first stage toward the downstream side (sucking oil at the second stage), pressurizing oil at the second stage, and discharging oil at the second stage.

In this manner, air (bubble) mixed with oil is ejected along with oil (as air-mixed oil) through the ejection port 24 which is faced to the upstream pump unit 70 at the first stage. Since density (mass) of the air (bubble) mixed with oil is small, air is easily collected at the inner side of the pump chamber P by the action of centrifugal separation. Accordingly, mixed air can be effectively ejected. Further, since the discharge rates Qu, Qd are set in consideration of the return rate (ejection rate Qe) to be returned to the oil pan OP through the ejection port 24, oil can be supplied (discharged) outside at the desired discharge rate Qd while achieving high pressurization with two-stage pressurizing action.

In the description of the above embodiment, the present invention is applied to the structure in which the rotor case 40 and the side plate 50 are arranged at the inside of the housing H (the housing body 10 and the housing cover 20) as a second housing. However, not limited to the above, the present invention may be applied to a structure without including the rotor case 40 and the side plate 50.

In the description of the above embodiment, the present invention is applied to the two-stage trochoid pump which includes the upstream pump unit 70 (the first inner rotor 71 and the first outer rotor 72) and the downstream pump unit 80 (the second inner rotor 81 and the second outer rotor 82). However, not limited to the above, the present invention may be applied to a structure including an inner rotor and an outer rotor of an internal gear type (involute type).

In the description of the above embodiment, the present invention is applied to a structure in which the housing H is separated into the housing body 10 and the housing cover 20. However, not limited to the above, the present invention may be applied to a structure in which a housing includes a first housing half body and a second housing half body which define a concave portion respectively.

In the description of the above embodiment, the oil pump of the present invention is adopted to an engine which is mounted on an automobile or the like. However, not limited to the above, an oil pump of the present invention may be adopted to a continuously variable transmission (CVT) or the like other than an engine.

As described above, according to an oil pump of the present invention, desired pumping performance can be ensured even if air or the like is mixed with oil to be sucked and pumping characteristics having desired high discharge pressure (discharge rate) can be achieved. Accordingly, in addition to be naturally adopted to an engine which is mounted on an automobile or the like, an oil pump of the present invention is useful for motorcycles, other vehicles having an engine mounted, continuously variable transmissions (CVTs) and other mechanisms requiring pressured feeding of lubricant oil, and the like.

Although a few embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents.

DESCRIPTION OF REFERENCE CHARACTERS

-   H Housing -   10 Housing body (Housing) -   11 Bearing hole -   12 Inner circumferential face -   13 End face -   14 Inlet passage -   15 Discharge passage -   16 Positioning hole -   17 Joint face -   18 Screw hole -   19 Positioning hole -   20 Housing cover (Housing) -   21 Bearing hole -   22 Concave portion -   23 Concave portion -   24 Ejection port -   Qe Ejection rate ejected from ejection port -   25 Circular hole -   26, 27 Positioning hole -   30 Rotary shaft -   S Axis line -   31 One end portion -   32 Other end portion -   33, 34, 35 Shaft portion -   40 Rotor case -   41 Cylindrical portion -   42 Inner circumferential face -   43 Inner circumferential face -   44 Middle wall portion (Partition member) -   44 a Bearing hole -   44 b Inlet port -   44 c Upstream discharge port -   44 d Downstream inlet port -   44 e Communication port -   45, 46 End face -   45 a, 46 a Positioning hole -   50 Side plate -   51 Circular hole -   52 Discharge port -   53 Positioning hole -   54 Concave portion -   60 O-ring -   70 Upstream pump unit -   Qu Discharge rate of upstream pump unit -   Wu Thickness of upstream pump unit in axis line direction -   P Pump chamber -   71 First inner rotor -   71 a Fitting hole -   72 First outer rotor -   L1 Axis line -   72 a Outer circumferential face -   80 Downstream pump unit -   Qd Discharge rate of downstream pump unit -   Wd Thickness of downstream pump unit in axis line direction -   81 Second inner rotor -   81 a Fitting hole -   82 Second outer rotor -   L2 Axis line -   82 a Outer circumferential face 

What is claimed is:
 1. An oil pump, comprising: an upstream pump unit which includes an upstream inner rotor and an upstream outer rotor; a downstream pump unit which includes a downstream inner rotor and a downstream outer rotor, the downstream inner rotor and the downstream outer rotor being arranged adjacently to the upstream pump unit in a predetermined axis line direction; a rotary shaft which concurrently rotates the upstream inner rotor and the downstream inner rotor; and a housing which contains the upstream pump unit and the downstream pump unit and supports the rotary shaft, the housing including an inlet port configured to suck oil from the outside into the upstream pump unit, an ejection port configured to eject a part of the sucked oil to the outside in a pressurization process of the upstream pump unit, a communication port which provides communication between the upstream pump unit and the downstream pump unit, and a discharge port configured to discharge oil from the downstream pump unit to the outside.
 2. The oil pump according to claim 1, wherein the upstream pump unit is configured to have a discharge rate that is larger than a discharge rate of the downstream pump unit.
 3. The oil pump according to claim 2, wherein the upstream pump unit has a discharge rate that is equal to a sum of a discharge rate of the downstream pump unit and an ejection rate ejected through the ejection port.
 4. The oil pump according to claim 3, wherein the ejection rate ejected through the ejection port is set to be 20% or more of the discharge rate of the upstream pump unit.
 5. The oil pump according to claim 1, wherein the upstream pump unit is configured to have a thickness in the axis line direction that is larger than a thickness of the downstream pump unit in the axis line direction.
 6. The oil pump according to claim 2, wherein the upstream pump unit is configured to have a thickness in the axis line direction that is larger than a thickness of the downstream pump unit in the axis line direction.
 7. The oil pump according to claim 3, wherein the upstream pump unit is configured to have a thickness in the axis line direction that is larger than a thickness of the downstream pump unit in the axis line direction.
 8. The oil pump according to claim 4, wherein the upstream pump unit is configured to have a thickness in the axis line direction that is larger than a thickness of the downstream pump unit in the axis line direction.
 9. The oil pump according to claim 1, wherein the housing comprises: a housing body which includes a concave portion for containing the upstream pump unit and the downstream pump unit; a partition member which is interposed between the upstream pump unit and the downstream pump unit; and a housing cover with which the housing body is covered.
 10. The oil pump according to claim 9, wherein the ejection port is arranged at the housing cover, the communication port is arranged at the partition member, and the inlet port is arranged at the partition member at a position opposite to the ejection port in the axis line direction as sandwiching the upstream pump unit.
 11. The oil pump according to claim 10, wherein each of the upstream pump unit and the downstream pump unit is a trochoid type having four blades and five nodes with the inner rotor and the outer rotor. 